Research On High Power Factor CRM Boost PFC Converter With All-Fixed Frequency Control Based On Variable Inductor

Boost PFC(Power Factor Correction)Converter has become one of the most widely used converters with its unique advantages,such as continuous input current,high output voltage,simple driving circuit,high power factor and so on.Among them,Critical conduction mode boost PFC converter can realize zero-current turn-on and have no diode recovery current.At the same time,the theoretical power factor reaches 1 under the traditional constant ontime(COT)control.So it is widely used in low-to-medium power fields.However,CRM boost PFC converter has a wide range in a half line cycle.When input voltage reaches 264 VAC,the range of switching frequency is as much as 15 times,which will increase the switching loss,reduce the converter efficiency and the design of EMI is more complex.To solve the problem that the range of the switching frequency is too large,the working principle of CRM boost PFC converter is deduced under the fixed frequency control(FFC).Compared with the constant on-time control,the fixed frequency control can realize the constant switching frequency in a half line cycle,but reduce the power factor.Therefore,this paper proposes a new control mode based on continuous variable inductance(CVI),which innovatively changes the inductance value with the change of electrical angle and the conduction time.And the switching frequency can be constant in the whole voltage range.The essence of CVI control is to transfer the pressure from the variation of large switching frequency to inductance value,but the existing variable inductance technology is difficult to achieve the required inductance.This paper further proposes a compromise scheme based on segment variable inductance(SVI).According to the theoretical derivation,the optimal subsection inductance value and electric angle of the highest power factor under different subsection numbers in a half line cycle are obtained,so as to ensure the constant switching frequency in a wide voltage range.In order to realize the required change of inductance in a half line cycle,the inductance model of a “double E” magnetic core is analyzed and designed in detail,the influence of main winding current and bias current under the change of inductance value is expounded,and the scheme of segment variable inductance is designed.Finally,a 120 W experimental prototype is built,and the experimental results verify the feasibility and effectiveness of the proposed method.